Explosive charge for oil wells



atente ct. 2?, 142

2,299,907 nmtosrva one son on. LLS

Application August 18, 1939, Semi N63. 296,735

13 Status. (CH. 52===5) Thisinvention pertains to the treatment of wells, and more particularly to an improvement in promoting the flow of materials, such as oil, from said wells.

The increase in flow of liquids from wells has been ordinarily eiiected by means of shooting, whereby an explosive charge at the proper position within the well is initiated, thereby causing enlargement of the diameter of the well hole as well as some separation of the strata along the bedding plates.

Heretoiore, because of the fact that it was considered essential to obtain the utmost bulk strength possible, that is to say the greatest potential strength per unit volume of the explosive charge, the application of explosives to oil wells and the like was restricted to liquid nitroglycerin and so-called "solidified nitroglycerin, which in effect is liquid nitroglycerin gelatinized by a minimum quantity of a suitable agent, namely nitrocellulose.

Although these types of explosives in general are satisfactory, they have certain outstanding defects; Thus liquid nitroglycerin, while it affords a high potential energy per unit of volume, 'detonates at a substantially constant rate of detonation regardless of how it is loaded. The rate of detonation of solidified nitroglycerin can be controlled to a certain extent by compression, as by tamping, for example. However, when the solidified nitroglycerin is used in wells of great material dispersed in an explosive liquid nitric ester present as a continuous liquid phase, said non-absorbent material being non-reactive with respect to said nitric ester. The texture of this product may vary from that of a liquid containing the-sparsely dispersed solids therein, to compositions at the other extreme containing much greater quantities of crystalline material and adequately characterized as being in the form of a slush. In other words, all of our compositions contain sufficient amounts of liquid nitric ester so that the latter remains in a fiowable state. The preferred liquid nitric ester for the purpose of our invention is nitroglycerin. In the following we shall discuss our invention in terms of this preferred embodiment.

The rate or velocity of detonation of the explosive charge can be controlled within the lim its desired for well-shooting by varying the amount of the non-absorbent, non-reactive crystalline ingredient employed per unit of explosive charge, or by using such ingredients as are inert with respect to the explosive reaction; that is they do not contribute substantially to the gas depth, which is not uncommon in the case of oil wells, the pressures prevailing at this depth may cause a compression of the solidified nitroglycerin 'to a point beyond its critical density, with the result that the material cannot be initiated. Such failures constitute an important factor in well-work, because, the work involved in removing the explosive charge not only is expensive and time-consuming, but in addition is quite hazardous.

The object of the present invention is an intproved explosive charge for use in wells. Another object is an explosive charge having a controllable rate of detonation when initiated at high pressures. A further object is an explosive charge which is sensitive to initiation at high pressures. blasting at elevated pressures, whereby the blasting efiect produced may be controlled. Other objects will become apparent as the invention is described hereinafter.

We have found that the foregoing objects are attained by employing an explosive charge comevolution of the charge upon its initiation, or still further by using various combinations of inert as well as active ingredients.

Although a decrease in the rate of detonation of an explosive charge is usually accompanied by a decrease in the bulk strength of the explosive, we have discovered that, so long as the bulk strength is not decreased imduly, said decrease produces no deleterious results in the shooting of wells. This observation is quite unexpected, in view of the fact that those engaged in the practice of shooting wells, as stated in the foregoing, have considered it essential to employ an explosive charge of maximum bulk strength.

The extent to which the bulk strength may be decreased without impairing the blasting action of the explosive charge is not subject to exact determination, since variations exist in the nature of the strata in different wells; hence it follows that an explosive charge may possess the requisite bulk strength for use in some wells, whereas the same charge is unsuited for use in other wells.

A still further object is a method of prising a crystalline substantially non-absorbent 55 By controlling the rate of detonation of the explosive charge by-variations in the composition of said charge, it is possible to produce the kind of blasting efiect best suited to the particular strata being blasted.

As the crystalline material non-reactive with respect to nitroglycerin, we prefer to employ salts which have a high solubility in water or which, upon initiation of the explosive charge, yield products that do not unite to form waterinsolublecompounds. This is due to the fact that the water-insoluble compounds by their presence tend to obstruct the flow of oil or similar material into the bore of the well.

In this connection, certain salts are quite de- Other salts which have been found desirable include those of the alkali metals, such as sodium nitrate, sodium chloride, and the like. I'he use of this group of salts is advantageous because,

ger of failure of initiation due to insensitiveness of said charge.

It will be understood that our invention does not preclude the use of ingredients having ac cepted value in explosive compositions. Thus a limited amount of carbonaceous material may be employed for the purpose of influencing the oxygen balance of the explosive charge, even though said carbonaceous material be capable of absorbing nitroglycerin. It is important to note, however, that in no instance do we contemplate the use of said carbonaceous material in amount sufflcient to interfere with the flowable condition of the amount of nitroglycerin present. Likewise, the use of essentially i ert materials, such made without departing from the spirit or scope even though some of them are not exceedingly v solublein water, they yield explosion-reaction products which are water-soluble.

Although all the foregoing salts are soluble in water to some extent, nevertheless an explosive composition containing these salts together with free liquid nitroglycerin may be employed satisfactorily in the presence of water. Apparently the nitroglycerin forms a water-impervious coating about the water-soluble salt and in this manner prevents any substantial joinder of said salt with the water. This characteristic is quite important in view of the fact that the methods commonly employed in well-shooting usually involve exposure of the explosive charge to water for appreciable time durations.

In rder to illustrate the efiect of some of these salts, on the rate of detonation of nitroglycerin, the following example is set forth.

i All charges had a diameter'of 1%" and were initiated with 100 gins. of 60% straight dynamite.

The foregoing tabulation illustrates the variations in velocity of detonation efl'ected by introduction of the various salts. A comparison oi explosives 2 and 3 indicates the degree of control in velocity which may be obtained by vari ation in the size of the grains *bf'salt.

It is of course known that the rate of detonation of solidified nitroglycerin can be regulated to some extent by varyin the tamping material employed to compress this material. However, as stated heretofore, the degree of regulation is limited by the fact that solidified nitroglycerin is characterized by a critical density which, if

' exceeded by means of tamping, high prevailing to l where elevated pressures prevail, without danof the invention. We intend, therefore, to be bound only in accordance with the following claims. r

We claim:

1. An explosive charge adapted for use in wells, comprising a water soluble inorganic salt, dispersed in a liquid explosive nitric ester present as a continuousflowable liquid phase said charge being free from absorbents the entire composi. tion being in flowable form,

2. An explosive charge adapted for use in wells, said charge comprising an explosive liquid nitric ester and a water soluble inorganic salt, at

being present as free flowable liquid the entire composition being in flowable form.

5. An explosive mixture adapted for use in wells, said mixture comprising an explosive liquid nitric ester and a water soluble inorganic salt capable of complete gasification upon initiation of the explosive mixture, at least a major portion of said nitric ester being present as flowable liquid the entire composition being in flowable form.

c. The explosive mixture or claim 5, wherein the substantially non-absorbent material is ammonium'nitrate.

'7. The explosive mixture of claim 5, wherein the substantiallynon-absorbent material is ammonium chloride. I

8. An explosive mixture adapted for use in well-shooting, said mixture comprising nitroglycerin, ammonium nitrate, and ammonium chloride, said nitroglycerin being present as flowable liquid.

9. An e'xplosive mixture adapted for use in well-shooting, said mixture consisting of 50 parts by weight of nitroglycerin, 25 parts by weight of ammonium nitrate, and 25 parts by weight of ammonium chloride the entire composition being in flowable form.

10. An explosive charge adapted for use in wells, said charge comprising a liquid explosive nitric ester and a water soluble inorganic salt, at least a major portion of said nitric ester being present as a flowable liquid and both unabsorbed and ungelatinous the entire composition being in flowable form.

11. An explosive charge adapted for use in wells comprising at least 50% of a liquid explosive nitric ester and a. water soluble inorganic salt dispersed in said liquid the entire composition being in flowable form.

12. An explosive charge adapted for use in wells comprising at least 50% of liquid nitroglycerin and ammonium nitrate dispersed in the same the entire composition being in fiowable form.

13. An explosive charge adapted for use in wells consisting essentially of a. liquid explosive nitric est/er present as a continuous flowable liquid phase-and ammonium nitrate dispersed in said liquid phase, the composition being free from absorbents the entire composition being in flowable form.

WALTER EASTBY LAWSON. I CLIFFORD A. WOODBURY. 

